Process for making, and an article of, porous cemented carbide



May 22, 1951 G. w. LUCAS 2,553,714

PROCESS FOR MAKING, AND AN ARTICLE 0F, POROUS CEMENTED CARBIDE FiledMarch 5, 194'? 2 Sheets-Sheet 1 ATTCRNEYS May 22, 1951 2,553,714

G. W. LUCAS PROCESS FOR MAKING, AND AN ARTICLE OF, POROUS CEMENTEDCARBIDE Filed March 5, 1947 2 Sheets-Sheet 2 GROU ND SURFACE LSFHEROIDALGRANULES DOINTED EDGE GROUND SURFACE? %volos IRREGULAR SHAPED PARTICLESATTORNEYS Patented May 22, 1951 PROCESS 'FORYMAKING, AND AN ARTICLE or,POROUS CEMENTED CARBIDE George W. Lucas, St. Clair Shores, Mich,assignoll' to Carboloy Company, Inc., a corporation of New YorkApplication March 5, 1947, Serial No. 732,581

I 4 Claims.

1 This invention relates to a process for making porous cemented carbideand articles of cement.-

. ed carbide having capillary porosity.

This invention contemplates a porous cement.- ed .carbide and a methodof producing the same, which has a high degree of hardness,wearresistance, and capillarity which makes this ma- ;terial especiallyuseful, for example, for bearings, drawing dies, and wear parts. Theporosity or capillarity of thematerial gives it the highly desirableability to retain, spread and transmit lubricant or coolant through thebody and over the wear orbearing surfaces thereof.

In the drawings:

Fig. 1 is a side elevation partly in vertical section of an apparatususeful in preparing my pcrous cemented carbide.

Fig. 2 is a section along the line .22 of Fig. 11.

Fig. 3 is aplan viewof my apparatus.

Figs. 4 and 5 are sketches illustrating the wear surface comparison ofmy porous cemented carbide made from spheroidal granules (Fig. 4) andconventional cemented carbide made from irregular shapedparticles (Fig.5).

In making my .porous :cemented carbides, I start with a powderconsisting of any of the well known hard metal carbides, such astungsten carbide, tantalum carbide, titanium carbide, and mixturesthereof, together with abinder metal of the iron group, such as cobalt,nickel or iron. When a mixture of tungsten carbide,

tantalum carbide and titanium carbide is used,

then preferably the tungsten carbide forms the larger component of saidmixture. Thepro'por tion of iron group .metal binder used can vary overa wide range but usually the iron group metal will not fall below 3% byweight of the cemented carbide composition. The

.can vary as taught by the Schroter Reissue Patent 17,624 and Schroter1,721,416, or over the wide range commonly used in the commercialproduction oftheabove cemented hardmetal carbides. The powder mixture ofhard metal carbides and iron group metal will be reduced by anyconventional method such, for example, as ballmilling, to an exceedinglyfine powder having .a grain size usually not exceeding 20 :microns, andpreferably well under-the 40 micron opening of-a. 325 mesh screen. Tothi fine powder mixture I add a small amount of temporary binder such as.parai'fin, carnauba wax, candelilla wax, or oneof the many petroleumwaxes, in an amount up to about 3% by weight. In addition small amountsof themoistening agent, suchas Water, acetone,

benzol, may be added if desired to facilitate converting the powderedmixture to a multiplicity of spherical or spheroidal particles.Preferably only sufficient temporary binder and moistening agent is usedto cause the grains of powder to agglomerate or adhere to each other toform spheres or spheroids while being processed. The term spheroid will.be used herein to include any spherical or substantially spherical oressentially round or spherical body. The converting of the powdered mixinto an aggregate of spheroidal bodies can be accomplished by anysuitable method such, for example, as by tumbling in acylindricalcontainer or by vibratory motion.

By way of example, I have illustrated one satisfactory apparatus forproducing spheroids from this powdered mixture. This apparatus comprisesa trough preferably inclined to the horizontal somewhere between 15 and.45. The trough l is preferably made from metal and positioned upon aflexible supporting frame generally designated 2. An electric vibrator3, producing a strong, substantially vertical upward impulse, indicatedby the arrow 4, is secured on the underside of trough I. Vibrator 3 canbe of any conventional make, but 1 preferably use an electric vibratorwhich is sold under the trade-name Syntron. This .electric vibratorcomprises in general a simple pulsating electromagnet and the air gapbetween the magnet and the armature of the vibrator is closed and openedevery cycle of the current setting up several thousand vibrations perminute. The heavy mass of the armature moving at such a high speedcauses a positive flow of powderful vibrations which are upwardlyapplied to the chute l in a vertical direction.

The powder and binder is spilled or flowed on to the trough l to give athin layer. The vibration causes the powder to move upwardly along theinclined chute, as indicated by the arrows, and the powder spills backupon itself as it travels up the curved return bent portion 5 of thechute, thus forming spheroids. The spheroid size is determined by theangle of the trough, intensity of vibration and amount of powder spilledinto the trough. The higher the degree of inclination the smaller thesperoids. Thus, when the trough'is inclined from the horizontal, thespheroids produced will be smaller than when the trough is inclined, atsay, 15 from the horizontal. It will be noted that the trough l inlongitudinal section resembles a toboggan.

The bottom of the trough I will preferably have a parabolic curve, asshown in section Fig. 2. The spheroids, generally designated 6,automatically roll down the trough where they are screened by screen andare collected in container 8. The spheroids are all coarser than a 325mesh screen opening and are comprised of thousands of individual powderparticles. Sizing of the spheroidal aggregates is easily eifected byscreen size separation. The selection of th size of aggregate dependsupon the degree of porosity desired in the finished product. Forexample, for a fine type of porosity aggregates which will pass througha 100 mesh screen opening and be deposited upon a 325 mesh screen andfor a coarser porosity aggregates which will pass through a mesh screenand collect upon a 100 mesh screen may be selected.

The spheroids thus formed are now subjected to complete sintering afterfirst being mixed with a material such as alumina powder or lamp blackwhich keeps the spheroids separated. The complete sintering consists ofsubjecting the spheroids first to pro-sintering at approximately 700 0.,followed by sintering at about 1400" C. for approximately fifteenminutes. Th sintering changes the soft powder spheroids or aggregatesinto hard, fully sintered spheroidal granules such as illustrated at 9,Fig. 4. The spheroids are of the same shap as the original powderaggregates but they are smaller in size due to mass shrinkage resultingfromsintering. Volumetrically the shrinkage is about 40%. The sinteredgrains are now separated from the enveloping medium (such as aluminapowder or lamp black) by screening, washing, or by air separation. Thesintered granules may, if desired, be further sorted by screen sizeoperation and are then ready for fabrication into the article desired.

To the spheroids which have been separated according to the siz desired,is now added a temporary binder such as paraffin, or one of the otherpetroleum or other waxes above mentioned. The sintered spheroids withtheir temporary binder are now pressed into their desired shape in aconventional steel mold and the pressure used will depend upon thepercentage of voids desired. The pressure may vary from about 2 to about30 tons per square inch. The spheroidal particles are thus brought intointimate contact with each other and are thereafter sintered whichcauses the particles to cement or fuse together at the points ofcontact. The resulting article, designated l6, Fig. 4, is comprised offirmly associated spheroids with the interstices between the granulesproviding voids of the capillary nature required. When the iron groupbinder is low, for example, from 3% to 6% by weight, it has been foundadvantageous to coat the spheroids with a thin layer of the iron groupmetal binder used in order to insure efficient fusing together at thepoints of contact. The coating of the spheroids with the iron groupmetal binder can be accomplished in any suitabl manner such, forexample, as by electrodeposition.

As an alternate method, the granules may be lightly compacted in agraphite mold of the desired shape and sintered therein under the samesintering conditions as before. This method is especially advantageouswhen spheroids of relatively coarse size are used, for example, thosewhich will pass a 20 mesh screen and collect upon a 100 mesh screen.Since the spheroids used in the final fabrication have been previouslyfully sintered, there is practically no additional shrinkage in thefinal sintering operation.

In articles made by the above-mentioned methods, thin oil is carriedvertically by capillarity, inch in 30 seconds. This material can beadvantageously used wherever a high degree of hardness, wear resistance,and self-lubrication by capillarity is desirable, for example, inbearings, drawing dies, and wear parts. Most applications of thismaterial use small spheroids, for example, somewhere between 20 and 325mesh, but for some applications it may be desirable to use largerspheroids, for example, spheroids having a diameter of anywhere fromabout .040 inch to about (.125) inch. Such spheroids can be made bymechanically pressing the powder to the size desired, or on the abovedescribed apparatus.

The chief advantages of a porous material made from sized spheroids isthe fact that the rounded contours of the particles 9 when ground to aflat surface ll offer no tendency to cause scuffing on the opposingsurface. This is not true of porous materials made from irregularshapedparticles (Fig. 5) for upon grinding such a material to a flat surface,jagged edges and pointed surfaces may easily present themselves at thewear surface. This may be easily seen from the accompanying drawingcomparing spheroidal and irregular-shaped particles. Other advantagesthat my material offers over solid cemented carbides are its oilretaining and spreading features plus its ability to transmit coolant orlubricant through the body of the material.

I claim:

1. A process for making porous cemented hard metal carbide articleshaving substantially continuous porosity comprising the steps of (l)forming spheroidal bodies by tumbling in the presence of a plasticizingagent a mixture of powdered hard metal carbide selected from the groupconsisting of tungsten carbide, titanium carbide, tantalum carbide andcombinations thereof in which tungsten carbide is the major componentand a powdered iron group metal, said hard metal carbide and said irongroup metal having a grain size not exceeding ZOmicrons in diameter, (2)fully sintering these spheroids, (3) selecting sintered spheroids havinga size falling within a range of from about 20 screen mesh to about 325screen mesh, (4) pressing a multiplicity of the said sintered spheroidsinto contact with each other and heating the same to a sinteringtemperature at which thesaid sintered spheroids fuse together at theirpoints of contact and maintain their identities as spheroids.

2. A process for making porous cemented carbide articles comprising thesteps of (l) mixing powdered hard metal carbideselected from the groupconsisting of tungsten carbide, titanium carbide, tantalum carbide andcombinations thereof in which tungsten carbide is the major componentand a powdered iron group metal, said powdered hard metal carbide andsaid iron group metal having a grain size of less than 20 microns, (2)mixing a plasticizing agent with the aforesaid mixture, (3) formingspheroidal bodies from the plasticized mixture by tumbling the saidpowdered mixture, (4) fully sintering the said spheroidal bodies intosound imporous hard metal carbide bodies having a size falling within arange of from about 20 screen mesh to about 325 screen mesh, (5)pressing a multiplicity of the said sintered bodies into contact witheachother and heating the same to a sintering temperature at which thesaid sintered bodies fuse together at their points of contact andmaintain their identities as spheroidal bodies.

3. A porous cemented hard metal carbide article produced by the processset forth in claim 1.

4. A porous cemented hard metal carbide article produced by the processset forth in claim 2.

GEORGE W. LUCAS.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Name Date Welch Nov. 24, 1931 Number OTHERREFERENCES Powder Metallurgy by Schwarzkorf, 1947, page 13.

2. A PROCESS FOR MAKING POROUS CEMENTED CARBIDE ARTICLES COMPRISING THESTEPS OF (1) MIXING POWDERED HARD METAL CARBIDE SELECTED FROM THE GROUPCONSISTING OF TUNGSTEN CARBIDE, TITANIUM CARBIDE, TANTALUM CARBIDE ANDCOMBINATIONS THEREOF IN WHICH TUNGSTEN CARBIDE IS THE MAJOR COMPONENTAND A POWDERED IRON GROUP METAL, SAID POWDERED HARD METAL CARBIDE ANDSAID IRON GROUP METAL HAVING A GRAIN SIZE OF LESS THAN 20 MICRONS, (2)MIXING A PLASTICIZING AGENT WITH THE AFORESAID MIXTURE, (3) FORMINGSPHEROIDAL BODIES FROM THE PLASTICIZED MIXTURE BY TUMBLING THE SAIDPOWDERED MIXTURE, (4) FULLY SINTERING THE SAID SPHEROIDAL BODIES INTOSOUND IMPOROUS HARD METAL CARBIDE BODIES HAVING A SIZE FALLING WITHIN ARANGE OF FROM ABOUT 20 SCREEN MESH TO ABOUT 325 SCREEN MESH, (5)PRESSING A MULTIPLICITY OF THE SAID SINTERED BODIES INTO CONTACT WITHEACH OTHER AND HEATING THE SAME TO A SINTERING TEMPERATURE AT WHICH THESAID SINTERED BODIES FUSE TOGETHER AT THEIR POINTS OF CONTACT ANDMAINTAIN THEIR IDENTITIES AS SPHEROIDAL BODIES.